The application of solid-state lighting, mainly refer to light-emitting diode (LED) as light source is becoming more and more popular in lighting industry due to its dimmable light level output, superior energy efficiency and longer operation lifetime. Same as incandescent, LED is an ideal light source for occupancy sensor control which can further enhance energy efficiency and operation lifetime because of its physical and electrical characteristics. Occupancy sensor is an electrical switching device used to provide automatic light control by sensing the occupancy status of a specific area with the applied sensing technology. Traditionally, a line voltage switching occupancy sensor is used to control LED light. However, conventional on and off switching control cannot bring the benefit and performance of LED light into full play, especially its dimming capability.
An LED light is mainly comprised of an LED module and an LED driver which is classified in constant current (CC) or constant voltage (CV) type. Traditional triac-type dimmer will not be able to control the dim status of the LED light because of its electrical characteristic different from incandescent light. Thus, a special and normally higher cost dimmable LED driver will be needed for a dimmable LED light. With reference to FIG. 6, an occupancy sensor 70 or other control device must provide a dim control signal, usually 0-10V, to the dimmable LED driver 60 to regulate the power output to the LED module 80. This requirement is apparently a negative factor against the efforts of reducing the overall cost of the LED light.
Since the occupancy sensor 70 can effectively further improve the energy efficiency of the LED light, it would be desirable to have an occupancy sensor which can operate with the DC power supply from the LED driver, either in type of constant current or constant voltage, and provide regulated DC power to control the output level of the LED module. It would be more desirable if an occupancy sensor is able to control the LED light in pre-determined dim output according to the occupancy status and ambient light level.
Conventional line voltage switching occupancy sensor 70 requires an electro-mechanical device, usually a power relay 71 having contacts, to switch the mains power applied on the light. The electric arc generated while relay contacts switching will gradually damage the relay contacts and shorten the life expectancy of electro-mechanical device, therefore results in sensor failure. Some LED drivers could also generate exceptionally high volume of inrush current while being switch on, disregard of the rated current output. Such a high inrush current could also damage the relay contacts after a period of operation time. Thus, an occupancy sensor without needing electro-mechanical device built-in will be more appropriate for LED light control.